I have a 1992 S10 Blazer. It is 4wheel drive, four door Tahoe version. It
has the 4.3 TBI with 354,000 miles on it.

The air seems to blow through the defrost all the time. Air does go through
the heater and vents but still comes through the defrost. I looked at the
heater assembly down by the floor and it looks like there is a hole in the
side where their used to be a screww or something. If I reach in and grab
the little arm inside that moves back and forth and stick a nail through the
hole and keep the arm from moving back, then I have full heat with very
little defrost. I can move to air and it does change from heat to air.

Is there a bracket or something that has fallen off? My wife and kids drive
it so they may have found something on the floorboard and tossed it.

I also have a vacumn leak on the controller but that as my fault not geting
it back together and aligned properly. I will redo that after fixing the
blower switch. It melts about once a year and I have to clean up the
contacts and put the switch back on.

--
Lannie


** Posted from http://www.teranews.com **

Sounds like a vacuum problem. I just did a complete tuneup on my
Blazer today and noticed one of my vacuum lines was old and decrepid
and had sucked itself shut. I redid the lines (one is a feeder line to
the heater control) and now my heater functions work like they should.
For a long time I could only get floor heat and hardly any defrost, I
believe this made a big difference but wont know for sure till I need
the defroster again....the heater directional functions (floor,
defrost or front panel) are vacuum controlled.


On Apr 21, 8:16*am, "Lannie Schafroth" <lannie at ct-iowa dot com>
wrote:

Lannie Schafroth wrote:
from floor to defrost is vacuum controlled. The default position of the
door is defrost. The leak means it stays on defrost.

--
Steve W.
Near Cooperstown, New York

On Apr 21, 8:21 pm, "Steve W." <csr684... (AT) yahoo (DOT) com> wrote:
had a 90 Blazer once with a similar problem and it had a broken
plastic clip in the bottom of the heater box that controlled the door
operation. It was(at the time) a GM only part(and may still be)and
hopefully it won't be discontinued at this point. It also was(WAS)
about a buck or so. If you suspect this(at some point), hopefully you
have a diagram of this system(or can get), take apart the lower part
of this 'ductwork' and look up from the bottom and hopefully(or not)
you'll see what I saw. Maybe it is what others have said it was and
if you have a leak near the control head, I would fix this FIRST but
after reading your issue-this(above) is what popped into my
mind(****). There is my two cents worth and today it is on sale for
FREE! Good luck-JP